The idea is that when you walk into a store that Shopkick partners with, you start to earn rewards -- "Kickbucks" -- just for walking in. (There's actually a device in the store that connects to your phone.) Its early partners include nationwide chains like Best Buy, American Eagle Outfitters, Macy's, and the Sports Authority, as well as shopping-mall outfit Simon Property Group.

Once you're inside the store, you can earn more Kickbucks for scanning in barcodes of products with your phone, and you can browse special offers. Kickbucks, in turn, can be redeemed for Facebook credits to play games online, song downloads, in-store gift cards, and other standard online rewards club stuff like magazine subscriptions or donations to charities.

Shopkick founder and CEO Cyriac Roeding

So basically Kickbucks is creating a rewards system; a portfolio of your shopping habits and the merchandise you find interesting enough to scan -- so it can potentially target you better with deals; and a virtual currency that can be redeemed for goods in the future.

Will it take off?

We're not sure how the rewards structure will look, which could play a big role. If it's a ripoff -- lots of activity required for lame rewards, it will get boring really quickly. But if it's actually a deal, then we could totally see teenagers or even adults tagging their way through stores by zapping barcodes with their iPhone cameras. (Shopkick would be smart to give people more incentives to tagging products, such as perhaps some sort of neat interactive diary of all the products you've tagged so far.)

Shopkick CEO Cyriac Roeding has several good things going for him: A great roster of early partners, who will need to push the app hard to get adoption, but could be rewarded with all the extra data; good buzz; and top-rate backers, including Kleiner Perkins' iFund, Greylock Partners, and LinkedIn founder Reid Hoffman.